This invention relates to a method of welding a soft-iron guide band to a steel projectile body.
It is known to affix a copper or a copper-zinc alloy guide band to a projectile body by arc welding. Since copper or copper-zinc alloys have a lower melting point than the steel of the projectile body, the bonding operation is equivalent to soldering since the steel surface is only very slightly melted if at all and is, in fact, not allowed to do so, otherwise the iron would mix with the copper melt. This would lead to an impermissible hardening of the guide band and thus would result in an increased wear of the weapon barrel. Upon firing from relatively long barrels of artillery pieces with large propellant charges, it has been found, however, that the guide bands have been worn out to such an extent as they pass through the barrel that the webs which form in the rifling profile have been entirely or almost entirely consumed. This may lead to an insufficient number of revolutions of the projectile and thus to an unstable flight, that is, to shortened trajectories with lateral deviations and, occasionally to a tumble of the projectile during flight.
It is known, as disclosed in German Offenlegungsschrift (application published without examination) 35 39 310 to mount guide bands made of copper-zinc alloys on thin-walled projectile bodies by means of flame or arc spraying to affect the thin-walled projectile body as little as possible. As an adherence layer for the guide band, for example, nickel aluminide or a cermet based on aluminum nickel oxide could be applied by spray-coating. Such a process, however, is relatively complex and expensive.
Therefore, instead of copper guide bands soft-iron guide bands have been used in order to achieve the desired properties, to thus ensure that the full guide band profile is preserved without significant changes even when the projectile is fired through a long barrel with a maximum propellant charge. If, however, the projectile body has a small wall thickness, pressing in the soft-iron guide band, as known from German Offenlegungsschrift 33 23 386 is not feasible. A securement of the soft-iron guide band by electron beam spot welding, in turn, leads to rusting underneath the guide band.
The electron beam welding, even if it is not a spot welding but is performed in the axial direction as it is known, for example, from German Offenlegungsschrift 40 39 956 for a guide band made of a copper-nickel alloy, leads to a significant hardening of the weld seam. This is so, because as the base alloy mixes with the soft iron, the resulting extremely rapid cooling in the melt zone leads to a martensite formation, possibly with fissures.